Monitoring cameras hitherto include monitoring cameras having a function of generating an alarm by utilization of a difference among movements of a subject captured by means of stationary cameras that perform neither panning nor tilting and cameras having a function of generating an alarm when the motion of a subject is not oriented in a given direction. Further, some monitoring cameras have a function of generating an alarm when a subject has approached a prohibited area by combining images captured by a plurality of stationary cameras that perform neither panning nor tilting. Patent Document 1 discloses that three-dimensional coordinates of a power transmission line, a steel tower, or a truck crane are determined by processing images captured by a plurality of stationary cameras; that a dangerous area is set around the power transmission line; and that, when the truck crane enters the dangerous area, an alarm is produced by monitoring a location of the truck crane.
Patent Document 1: JP-A-6-347220